Aliphatic polyesters have been noticed as a material capable of exhibiting a biodegradability. Further, as a part of the aliphatic polyesters, plastics derived from biomasses instead of the conventional petroleum base materials have been developed and noticed as a material that is effective to take measures against global warming problems, and provides an alternative material for petroleum resources which are expected to be exhausted in future.
However, the aliphatic polyesters not only exhibit problems such as a high hydrolyzability and a poor retention of properties, i.e., a poor durability, under high-temperature and high-humidity conditions, but also undergoes a large limitation to applications thereof when the aliphatic polyesters are used alone, because they generally have a low impact resistance. Therefore, for the purpose of improving an impact resistance of the aliphatic polyesters, there have been proposed a composition comprising a polylactic acid and a modified olefin compound (Patent Document 1); a composition comprising an aliphatic polyester and syndiotactic polypropylene (Patent Document 2); and further a composition comprising a polylactic acid and an ethylene-propylene-diene (EPDM)-based thermoplastic elastomer (Patent Document 3). However, these conventional compositions have failed to exhibit a sufficient effect of improving an impact resistance thereof, and further have such a problem that injection-molded products obtained from these conventional compositions tend to suffer from delamination phenomenon. In addition, the conventional compositions also have a less effect of improving a durability thereof.
On the other hand, the aliphatic polyesters are readily electrically charged and, therefore, have limitations to the applications in which electrostatic disturbance is expected. To solve the above problem, there has been proposed a method of blending an aliphatic polyester, in particular, a polylactic acid, with a nonionic surfactant comprising a glycerol aliphatic polyester to improve an destaticizing property thereof (Patent Document 4). In addition, there has been proposed a method of blending a biodegradable resin with a specific anionic surfactant (Patent Document 5). However, these conventional methods have such a problem that the resulting compositions are insufficient in not only antistatic property but also persistency of the antistatic property. Further, the aliphatic polyesters exhibit a poor durability because they tend to be deteriorated in strength under high-temperature and high-humidity environmental conditions.
Patent Document 1: Japanese Patent Application Laid-Open (KOKAI) No. 9-316310 (1997)
Patent Document 2: Japanese Patent Application Laid-Open (KOKAI) No. 10-251498 (1998)
Patent Document 3: Japanese Patent Application Laid-Open (KOKAI) No. 2002-37987
Patent Document 4: Japanese Patent Application Laid-Open (KOKAI) No. 10-36650 (1998)
Patent Document 5: Japanese Patent Application Laid-Open (KOKAI) No. 2005-264159